Left atrial pressure is a measure of a patient's volume status, and serves as a guide to the use of fluid, diuretic, and vasopressor therapy in patients with congestive heart failure, shock, and various other hemodynamic derangements. Left atrial pressure conventionally is measured invasively, by transvenous placement of a pulmonary artery catheter, with the pulmonary artery wedge pressure taken as an indirect reflection of left atrial pressure. This invasive measurement technique entails considerable cost and some potential morbidity. Total vascular resistance is a measure of a patient's vascular tone and is used to aid management of shock states. Ordinarily it is measured by obtaining simultaneously a cardiac output (from an indwelling thermodilution pulmonary artery catheter) and an arterial pressure from an indwelling intra-arterial catheter). Advances in the state of the art of cross-sectional and Doppler echocardiography have permitted the formulation of techniques for non- invasive calculation of left atrial pressure and total vascular resistance. These techniques have not yet been validated, however, in a critical care unit patient population. In the past two years, we have performed bedside echocardiography in approximately 60 patients for the purpose of validating these techniques. the conventional measurement of cardiac output from suprasternal Doppler echocardiography has been proven to be invalid in critically ill patients, and a modified apical Doppler technique has been adopted. Should be modified techniques prove sufficiently precise, they have promise as an investigative tool in subsequent studies of fluid, sufficiently precise, they have promise as an investigative tool in subsequent studies of fluid, vasopressor, and vasodilator therapy both n critical care units and in ambulatory patient populations.